Catalytic Dehydrogenation Of Ammonia Borane By Palladium Phosphating Catalyst And Simulation Of Hydrogen Storage Tank

The use of hydrogen energy includes the preparation,purification,storage,transportation and use of hydrogen.The rapid development of fuel cell vehicles will further promote the wide application of hydrogen energy.The safe storage and controlled release of hydrogen is one of the factors restricting the promotion of hydrogen fuel cell vehicles.Ammonia borane（NH₃BH₃,AB）,with hydrogen content up to 19.6wt%,is stable at room temperature and has good environmental friendliness.It is considered as a potential chemical hydride hydrogen storage material.Under the right catalyst,3 mol hydrogen can be produced per mole of ammonia borane hydrolysis,which is considered to be the most convenient dehydrogenation method of ammonia borane.The development of efficient,economical and stable catalysts is of great significance to the popularization and practical application of ammonia borane.So far,precious metals,non-precious metals and their composites have been widely used to catalyze the hydrolytic dehydrogenation of AB.Noble metal catalyst has high catalytic activity but high price,while non-noble metal catalyst is cheap but low activity.Therefore,reducing the use of noble metal and improving the catalytic activity of non-noble metal is of great significance to the practical application of hydrogen storage system.The precious metal palladium belongs to the platinum group,which has similar catalytic activity but is much cheaper than platinum.Transition Metal Phosphides（TMPs）have semi-metallic properties which are stable in acid and base environments and have excellent photothermal stability.TMPs is a novel catalytic material which shows similar catalytic activity to precious metal platinum in hydrodesulfurization（HDS）and hydrogen evolution（HER）reactions.Recently,researchers have found that TMPs show high catalytic activity in the hydrolytic dehydrogenation of ammonia borane,and the catalytic activity of transition metals can be greatly improved by doping non-metallic P.Graphene,on the other hand,is a one-atom thick carbon material with large specific surface area,strong mechanical strength,thermodynamic and chemical stability,and excellent charge fluidity,making it an ideal carrier material for the growth and dispersion of metal nanoparticles.At present,high-pressure gaseous hydrogen storage is a relatively mature vehicle hydrogen storage technology,but its hydrogen storage density is low,the pressure is high,transportation and filling process has the risk of leakage,has a certain security risks.Using ammonia borane as hydrogen storage carrier can avoid these problems.In order to enable the hydrogen generated by catalyzed ammonia borane to be applied to fuel cell vehicles,this paper proposes a combined hydrogen supply system of"chemical hydrogen storage+physical hydrogen storage":The main function of the chemical hydrogen storage part is to catalyze ammonia borane to produce hydrogen,and the main function of the physical hydrogen storage part is to temporarily store the hydrogen generated by the compressor in the hydrogen storage tank,which can provide hydrogen for the fuel cell at any time.The combined hydrogen supply system can reduce the hydrogen storage tank pressure,improve hydrogen storage density and hydrogen storage safety.Based on this,this paper developed two graphene-supported palladium transition metal phosphating catalysts for ammonia borane dehydrogenation,and studied the"chemical hydrogen storage+physical hydrogen storage"combined hydrogen supply system by simulation.The main research work is as follows:（1）Orange-shaped Pd@Co@P nanoparticles supported by reduced graphene oxide（r GO）were synthesized by one-pot co-reduction at room temperature using methylaminoborane（Me AB）as reducing agent and Pd Cl₂,Co Cl₂and Na H₂PO₂as precursors.The synthesized Pd@Co@P/r GO NPs has good catalytic activity and cyclic stability for the hydrolytic dehydrogenation of AB,and the TOF of the synthesized Pd₁@Co_7.5@P₂₅/r GO catalyst is 127.57 min^-1.The TOF of Pd@Co/r GO catalyst without doping P is 37.38 min^-1.The activation energy Ea of Pd₁@Co_7.5@P₂₅/r GO is 39.05 k J·mol^-1,which further indicates that Pd@Co@P/r GO has higher catalytic activity and better catalytic kinetic performance.（2）Using MeAB as reducing agent and PdCl₂,NiCl₂and NaH₂PO₂as precursors,the reduced graphene oxide supported Pd@Ni P core-shell nanoparticles were synthesized by one-step method and used as efficient and stable ammonia borane catalyst for hydrogen production.Firstly,Pd@Ni P/r GO core-shell nanoparticles were synthesized and characterized.Due to the effective doping of P and the synergistic electronic effect between Ni and P,the synthesized Pd@Ni P/r GO nanoparticles exhibit stronger catalytic activity than the phosphorus-free nanoparticles during the hydrolysis of ammonia borane.The catalyst has excellent catalytic activity,with a TOF value of 133.33 min^-1and activation energy（Ea）of 29.31 k J·mol^-1.This simple and fast synthesis method can also be extended to other graphene-supported transition metal phosphating core-shell nanoparticles.（3）according to the present vehicle hydrogen storage problem put forward the"chemical hydrogen storage+physical hydrogen storage for hydrogen joint system,based on Simulink and COMSOL simulation software to build the hydrogen storage model,the above experiment of ammonia borane hydrolysis rate of hydrogen production as parameters into the model to calculate,simulate joint under three conditions for hydrogen system running status,It can run smoothly in these three working conditions,and the gas temperature in the hydrogen storage tank still does not exceed the safety temperature of 358.15 K even in the comparative limit case,indicating that the combined hydrogen supply system of"chemical hydrogen storage+physical hydrogen storage"has high safety.The parameters of hydrogen storage tank were studied by means of control variable method,and the effects of different inlet rate,inlet temperature,initial hydrogen pressure and ambient temperature on the thermal effect of hydrogen storage tank during charging and discharging were investigated.The results show that pre-cooling inlet temperature,decreasing inlet rate and increasing initial pressure can reduce the thermal effect during charging and discharging cycle of high-pressure hydrogen storage tank,and reduce hydrogen temperature,thus greatly improving the safety of hydrogen storage tank.